Piston for internal-combustion engine and method for manufacture thereof

ABSTRACT

A piston 1 made of an aluminum alloy was cast in a manner to enclose a ringlike member 6 of a three-layer structure having aluminum alloy materials 8 disposed on both sides of a copper alloy material 7, at a piston&#39;s peripheral portion 2 forming thereon piston ring grooves 3 of the piston 1. The ringlike member 6 and the piston 1 are monolithically bonded together by a local remelting of the aluminum alloy material 8 of the ringlike member 6 and the piston 1 at a bonded portion thereof. Then, a piston ring groove 3 was formed on the copper alloy material 7 of the ringlike member 6. With this, it is possible to obtain an internal-combustion engine&#39;s piston that does not have adhesion of a hardened layer portion forming thereon a piston ring, to the piston ring, and does not have cracks on the hardened layer.

TECHNICAL FIELD

The present invention relates, for example, to a piston of an automotiveinternal-combustion engine, particularly to a piston provided with apiston ring groove that is superior in adhesion to the piston ring andin abrasion resistance, and relates to a method for producing the same.

BACKGROUND TECHNOLOGY

A piston for internal-combustion engine is generally made of aluminumalloy, and its peripheral portion is formed with a plurality of pistonring grooves. A piston ring is fitted in this piston ring groove. Of thepiston ring grooves, the top ring groove, in which the top ringpositioned nearest to the crown surface is fitted, tends to haveabrasion on its inner surface, because of the reasons that thetemperature is high due to its close position to the combustion chamberand that the top ring receives the combustion pressure, and because ofother reasons.

As a countermeasure against this, Japanese Patent Laid-open Publication2-125952 proposes an aluminum alloy piston prepared by forming aperipheral groove on a peripheral portion forming thereon a piston ringgroove, then by fitting into the peripheral groove a copper wirematerial wound thereon, and then by locally melting the copper wirematerial and its neighboring piston base material by electron beam, thenby allowing the melted copper to diffuse into the piston base material,thereby to form an abrasion-resistant hardened layer made of an alloy ofaluminum alloy and copper, having a copper content of 10-35 wt %, andthen by forming the piston ring groove on the hardened layer.

According to the above-mentioned conventional example, however, the areaof the primary crystal layer is large in a hardened layer's region whichhas a small copper content. Therefore, it tends to adhere to a cast-ironpiston ring during the driving of the internal-combustion engine.Furthermore, the amount of an intermetallic compound of aluminum alloyand copper becomes large in a region having a large copper content.Thus, the hardened layer may have cracks due to thermal stress after theelectron beam irradiation.

As a countermeasure against this, it is supposed to melt only a bondedportion between a piston base material and a composite material formedfrom a copper-containing powder compact, in place of the copper wirematerial, and to form a piston ring groove on the composite material asthe hardened layer superior in abrasion resistance. In this case,however, a low-melting-point binder powder of the powder compactvaporizes by the electron beam irradiation. Therefore, it is difficultto conduct a melt adhesion between the piston base material and thecomposite material, and thus it can not be adopted offhand.

The present invention was made in view of the above-mentioned problemsof conventional technologies. Its object is to provide a piston forinternal-combustion engine, having a piston ring groove superior inabrasion resistance, and a method for producing the same, without havingadhesion of a hardened layer portion, which forms thereon a piston ring,to the piston ring, and without having cracks on the hardened layer.

DISCLOSURE OF THE INVENTION

According to a piston for internal-combustion engine of the invention, aringlike member of a three-layer structure having aluminum alloymaterials disposed on the both sides of a copper alloy material has beenembedded in a peripheral portion forming thereon a piston ring groove ofan aluminum alloy piston. Furthermore, a remelting portion has beenformed at a bonded portion between the aluminum alloy material of thisringlike member and the piston, and thus the ringlike member and thepiston has been bonded together monolithically. Still furthermore, thepiston ring groove has been formed on the copper alloy material of theringlike material.

Furthermore, according to the invention, the copper alloy material ofthe ringlike material was formed by an aluminum bronze material.

Furthermore, as the copper alloy material of the ringlike member, acomposite material was formed from a powder compact prepared by adding10-15 wt % of silicon carbide and 15-20 wt % of aluminum bronze to abinder powder of silicon and aluminum.

Still furthermore, the ringlike member is heated at a certainpredetermined temperature and pressurized at a certain predeterminedpressure, and thus there is a metal bond between the copper alloymaterial and the aluminum alloy material of the ringlike member.

According to the invention, a ringlike member of a three-layer structurehaving aluminum alloy materials disposed on both sides of an iron alloymaterial has been embedded in a peripheral portion forming thereon apiston ring groove of an aluminum alloy piston. Furthermore, a remeltingportion has been formed at a bonded portion between the aluminum alloymaterial of this ringlike member and the piston, and thus the ringlikemember and the piston have been bonded together monolithically. Stillfurthermore, the piston ring groove has been formed on the iron alloymaterial of the ringlike material.

A method for producing a piston according to the invention comprises afirst step of casting a piston in a manner to enclose a ringlike memberof a three-layer structure having aluminum alloy materials disposed onboth sides of a copper alloy material, at a peripheral portion formingthereon piston ring grooves of the piston made of aluminum alloy; asecond step of monolithically bonding the ringlike member and the pistontogether by a local remelting of the aluminum alloy material of thisringlike member and the piston at their bonded portion; and a third stepof forming a piston ring groove on the copper alloy material of theringlike member.

Furthermore, the local remelting at the bonded portion between thealuminum alloy material of the ringlike member and the piston basematerial is conducted by the electron beam irradiation in a vacuumatmosphere. The electron beam may be replaced with laser beam. In thiscase, the operation in the atmosphere becomes possible.

Herein, the bonded portion between the aluminum alloy material of theringlike member and the piston base material is rapidly cooled down bythe piston base material after the electron beam irradiation, that is,after the passage of the electron beam. However, since a brittle alloylayer is not formed on the bonded portion between the aluminum alloymaterial of the ringlike member and the piston base material, no cracksoccur thereon.

After that, the outer shape of the piston is formed, and the piston ringgroove is formed on the copper or iron alloy material portion as thehardened layer of the ringlike member which is superior in abrasionresistance.

Due to this, according to the invention, there is obtained a piston forinternal-combustion engine that is capable of forming thereon a pistonring groove superior in abrasion resistance, without having adhesion ofthe hardened layer having the piston ring groove formed thereon, thatis, the copper alloy material portion of the ringlike member, to apiston ring, and without having cracks on the copper or iron alloymaterial portion as the hardened layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1a is a sectional view showing an essential portion of a piston forinternal-combustion engine according to an embodiment of the presentinvention;

FIG. 1b is an enlarged sectional view showing a piston ring groove ofthe piston;

FIG. 2 is an explanatory view of a press;

FIG. 3 is an explanatory view showing that a ringlike member is obtainedfrom a blank material;

FIG. 4 is a perspective view showing the ringlike member;

FIG. 5 is an explanatory view showing a mold for casting a piston; and

FIG. 6 is an explanatory view showing a condition of the electron beamirradiation.

BEST MODE FOR CARRYING OUT THE INVENTION

In the following, the best mode for carrying out the present inventionwill be described in detail, based on the drawings.

FIG. 1a is a sectional view showing an essential portion of a piston forinternal-combustion engine according to an embodiment of the presentinvention, and FIG. 1b is an enlarged sectional view showing a pistonring groove of the piston. In the drawings, designated by numeral 1 is apiston for internal-combustion engine. This piston 1 is made of a highsilicon aluminum alloy material (e.g., JIS AC8A material). A peripheralportion 2 of a crown portion 1a of this piston 1 is formed with aplurality of piston ring grooves, that is, a top ring groove 3, a secondring groove 4, and an oil ring groove 5.

Of the piston ring grooves 3, 4 and 5, the top ring groove 3 is formedon the ringlike member 6 embedded in the peripheral portion 2 formingthereon the piston ring groove 3. In detail, the ringlike member 6 isformed of a three-layer structure having aluminum alloy materials 8disposed on both sides of a copper alloy material, and the top ringgroove 3 is formed on the copper alloy material portion 7 of theringlike plate member 6.

The above-mentioned piston is formed, as follows.

At first, a process for forming the ringlike member 6 will be explained.That is, a blank material 9 having plate-like aluminum alloy materials 8disposed on both sides of a plate-like copper alloy material 7 is heatedat a temperature that is somewhat higher than the recrystallizationtemperature of the aluminum alloy material 8 in a furnace not shown inthe drawings. Furthermore, it is interposed between an immobile board 11and a mobile board 12 of a press 10 shown in FIG. 2 and pressurized at acertain predetermined pressure. With this, the three plate members ofthe copper alloy material 7 and the aluminum alloy materials 8 of theblank material 9 are united into a monolithic body by metallic bondthrough diffusion. In FIG. 2, designated by numerals 13, 14 and 15 are acylinder device, a ram, and a column, respectively.

Then, as shown in FIG. 3, the blank material 8 is blanked out with apress or the like, thereby to obtain the ringlike member 6 having athree-layer structure as shown in FIG. 4.

In the following, a process for molding the piston 1 by casting will beexplained.

At first, as shown in FIG. 5, the ringlike member 6 is disposed at acertain predetermined position in a casting mold 16 for forming thepiston 1, that is, the peripheral portion 2 forming thereon the pistonring groove 3 of the piston 1. In this embodiment, the ringlike member 6is disposed on a step portion 17 formed in the casting mold 16. Then, amelted alloy is supplied into the casting mold 16 through a gate 18.With this, the piston 1 is cast, and at the same time the ringlikemember 6 is enclosed by the melted alloy (the first step).

The piston having the ringlike member enclosed by the melted alloy istaken out of the casting mold 16. Then, as shown in FIG. 6, it isirradiated with the electron beam 18 in a vacuum atmosphere. With this,the aluminum alloy material 8 of the ringlike member 6 and the piston 1are melted locally at their bonded portion, and thus the ringlike member6 and the piston 1 are bonded together into a monolithic body (thesecond step).

As shown in FIG. 6, the electron beam irradiation is conducted, whilethe piston 1 is rotated at a slow speed. Therefore, the melted portionis rapidly cooled down by the base material of the piston 1 after theirradiation with the electron beam 18, that is, after the passage of theelectron beam 18.

After that, an outer shape of the piston 1 is formed, and as shown inFIG. 1, the piston ring groove 3 is formed on the copper alloy materialportion 7 of the ringlike member 6 (the third step).

With this, there is obtained a piston 1 for internal-combustion enginewhich is capable of forming a piston ring groove superior in abrasionresistance, without having adhesion of the hardened layer formingthereon the piston ring groove 3, that is, the copper alloy materialportion 7 of the ringlike member 6 in this embodiment, to the pistonring, and without having cracks on the copper alloy material 7.

EMBODIMENT

Good results were obtained by adopting the following concrete structureof the ringlike member 6.

(1) An aluminum bronze material having a texture where analuminum-copper intermetallic compound is dispersed in a copper base wasused as the copper alloy material 7, and an aluminum alloy extensiblematerial 4032 was used as the aluminum alloy material 8.

In fact, aluminum alloy extensible materials 4032 according to JapaneseIndustrial Standard were disposed on both sides of the aluminum bronzematerial. The blank material 9 under this condition was heated at about600° C. and furthermore pressurized at a pressure from about 600 to 700MPa.

Then, the ringlike member 6 was formed from the blank material 9.

(2) A composite material formed from a powder compact was used as thecopper alloy material 7, and an aluminum alloy extensible material 4032according to Japanese Industrial Standard was used as the aluminum alloymaterial 8.

In fact, a composite material was formed by forging a powder compactprepared by adding 10-15 wt % of silicon carbide and 15-20 wt % ofaluminum bronze to a binder powder of silicon and aluminum, with theaddition of pressure. The content (wt %) of the binder powder of siliconand aluminum is relatively defined, relative to the weight percentage ofsilicon carbide and aluminum bronze of the above-mentioned certainpredetermined range, and the total is defined as being 100 wt %. Then,the aluminum alloy extensible materials 4032 according to JapaneseIndustrial Standard were disposed on both sides of the compositematerial as the copper alloy material 7, and the blank material 9 underthis condition was heated at about 600° C., and furthermore pressurizedat a pressure from about 600 to 700 MPa.

Then, the ringlike member 6 was formed from the blank material 9.

According to the present invention, it is possible to form a piston ringgroove superior in abrasion resistance, without having adhesion of thehardened layer having the piston ring groove formed thereon, that is,the copper or iron alloy material of the ringlike member, to a pistonring, and without having cracks on the hardened layer. Therefore, it ispossible to obtain an internal-combustion engine's piston having asuperior durability.

INDUSTRIAL APPLICABILITY

As mentioned hereinabove, an internal-combustion engine's piston and amethod for producing the same according to the present invention are notlimited to the above-mentioned embodiment. For example, the copper alloymaterial of the ringlike member may be replaced with an iron alloymaterial. Furthermore, it can surely be applied to aninternal-combustion engine's piston for watercraft and the like, as wellas that for automobile.

What is claimed is:
 1. A piston for an internal-combustion engine, whichis characterized in that a ringlike member of a three-layer structurehaving aluminum alloy materials disposed on both sides of a copper alloymaterial has been embedded in a peripheral portion forming thereon apiston ring groove of an aluminum alloy piston, that a remelting portionhas been formed at a bonded portion between said aluminum alloy materialof this ringlike member and the piston, thereby to bond together theringlike member and the piston monolithically, and that the piston ringgroove has been formed on the copper alloy material of the ringlikematerial.
 2. A piston for an internal-combustion engine according toclaim 1, which is characterized in that the copper alloy material of theringlike member is made of an aluminum bronze material.
 3. A piston foran internal-combustion engine according to claim 1, which ischaracterized in that the copper alloy material of the ringlike memberis a composite material formed from a powder compact prepared by adding10-15 wt % of silicon carbide and 15-20 wt % of aluminum bronze to abinder powder of silicon and aluminum.
 4. A piston for aninternal-combustion engine according to claim 1, which is characterizedin that the copper alloy material and the aluminum alloy material havebeen heated at a certain predetermined temperature and pressurized at acertain predetermined pressure such that there is a metal bond betweenthe copper alloy material and the aluminum alloy material.
 5. A methodfor producing a piston of an internal-combustion engine, said methodcomprising:a first step of casting a piston made of an aluminum alloy ina manner to enclose a ringlike member of a three-layer structure havingaluminum alloy materials disposed on both sides of a copper alloymaterial, at a piston's peripheral portion forming thereon piston ringgrooves; a second step of monolithically bonding the ringlike member andthe piston together by a local remelting of the aluminum alloy materialof this ringlike member and the piston at a bonded portion thereof; anda third step of forming a piston ring groove on the copper alloymaterial of the ringlike member.
 6. A method for producing a piston ofan internal-combustion engine according to claim 5, which ischaracterized in that the local remelting of the aluminum alloy materialof the ringlike member and the piston base material at the bondedportion is carried out by an electron beam irradiation in a vacuumatmosphere.
 7. A method for producing a piston of an internal-combustionengine according to claim 5, which is characterized in that the localremelting of the aluminum alloy material of the ringlike member and thepiston base material at the bonded portion is carried out by a laserbeam irradiation in the atmosphere.